doc: De-duplicate readme and license files

The readme.rst and license.rst files in the project root overlap
with the index.rst and license.rst files in the docs/ folder. We
need to use the latter when building the documentation, as Sphinx
requires all included files to be under a common root. However,
the files in the root are currently used by the cgit and Github
viewers.

Using symlinks in Git presents some difficulties so the best
course of action is likely to leave these files but in stub form.

The license.rst file in the root will simply tell the reader to
refer to docs/license.rst.

The readme.rst file will contain a small amount of content that
is derived from the docs/index.rst file, so that the Github main
page will have something valid to show, but it will also contain
a link to the full documentation on ReadTheDocs.

Change-Id: I6dc46f08777e8d7ecb32ca7afc07a28486c9f77a
Signed-off-by: Paul Beesley <paul.beesley@arm.com>
diff --git a/docs/index.rst b/docs/index.rst
index 268ac47..4f0f6ef 100644
--- a/docs/index.rst
+++ b/docs/index.rst
@@ -43,10 +43,9 @@
 Users are encouraged to do their own security validation, including penetration
 testing, on any secure world code derived from TF-A.
 
-Arm will continue development in collaboration with interested parties to
-provide a full reference implementation of Secure Monitor code and Arm standards
-to the benefit of all developers working with Armv7-A and Armv8-A TrustZone
-technology.
+In collaboration with interested parties, we will continue to enhance |TF-A|
+with reference implementations of Arm standards to benefit developers working
+with Armv7-A and Armv8-A TrustZone technology.
 
 Functionality
 -------------
@@ -133,8 +132,8 @@
    The use of pointer authentication in the normal world is enabled whenever
    architectural support is available, without the need for additional build
    flags. Use of pointer authentication in the secure world remains an
-   experimental configuration at this time and requires the ``ENABLE_PAUTH``
-   build flag to be set.
+   experimental configuration at this time and requires the
+   ``BRANCH_PROTECTION`` option to be set to non-zero.
 
 -  Position-Independent Executable (PIE) support. Initially for BL31 only, with
    further support to be added in a future release.